Are the magnets in speakers strong?
I would say yes, in general, they're going to be a lot stronger than most of the crappy things sold as fridge magnets. That's why, when I happened upon a giant box of small speakers when my work was cleaning out old junk, I took the whole box home, and now I have a near-infinite supply of really excellent fridge magnets. I'll even mail you some if you send a SASA, so you can check 'em out. Send me email/message for more info. This offer only open to OP, sorry! :-) As for the magnets in larger car speakers (6x9s, 5s, 10s, 12s, 15s) -- they're not as strong by mass, but still super strong. If you are looking for strong magnets, the best are usually based on neodymium.
There are different magnetic materials in existance each with their own strength. One of the strongest are rare earth (neodymium) magnets found in hard disk drives. Most speakers use AlNiCo magnets, not as strong as neodymium. I've used both to strengthen some old cabinet magnets to keep the doors closed and other various uses.
Depends on speaker. If you use some standart Magnat speaker magnet, it is surprisingly weak - it cannot catch and hold some screws!!! so so weak. But it is only way to see how strong is the magnet overall - the strongest magnet is really neodymium, but the strongest speaker (strong motor) is propably PD (precision devices) 1851 which is not selled today. People who has heard this speaker saying, that it's like to be hit with baseball bat when it produced bass sounds. They say that you had to have some kind of weapon licence to have this speaker :-) The strongest (now selling) is this I guess: eshop dance.cz/DetailPage.asp?. BL( force factor) over 34, 6 voice coil and huge (looks like 12) magnet goes to crush your head. It is not maybe the strongest magnet ever created, but it pushes and drives its voice coil like no other speakers. MTX jackhammer is only funny piece of crap against this.
